Here are the macros.
Arcane Shot + Aspect of the Hawk
#showtooltip Arcane Shot
/startattack
/castsequence reset=1 !Aspect of the Hawk, null
/cast Arcane Shot
This macro will cast Aspect of the Hawk when you cast an Arcane Shot. This is due the fact that you might be in Aspect of the Fox and lose the dmg bonus.
Cobra Shot + Aspect of the Fox
#showtooltip Cobra Shot
/startattack
/castsequence reset=1 !Aspect of the Fox, null
/cast Cobra Shot
More macros
This can be used also for Steady Shot, Marksman spec by replacing the names. Will cast Aspect of the Fox when Cobra Shot is being casted. Not really useful in PVE since you can be stationary and still cast Cobra Shot. This is viable only for PVP and some PVE situation.
Kill Command + Aspect of the Hawk
#showtooltip Kill Command
/startattack
/castsequence reset=1 !Aspect of the Hawk, null
/cast Kill Command
/script UIErrorsFrame:Clear();
This is great in PVP and PVE, can also be used for Chimera Shot when playing Marksman. The only issue is that Chimera shot has a long cooldown is is better to have /stopcasting macroed and this makes the Aspect macro buggy.
Using these macros you can free two buttons that were assigned for switching aspects.